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<FONT color="green">001</FONT>    // Copyright 2008 Regents of the University of California.  May be used<a name="line.1"></a>
<FONT color="green">002</FONT>    // under the terms of the revised BSD license.  See LICENSING for details.<a name="line.2"></a>
<FONT color="green">003</FONT>    package org.joe_e.var;<a name="line.3"></a>
<FONT color="green">004</FONT>    <a name="line.4"></a>
<FONT color="green">005</FONT>    import java.io.Serializable;<a name="line.5"></a>
<FONT color="green">006</FONT>    <a name="line.6"></a>
<FONT color="green">007</FONT>    import org.joe_e.Equatable;<a name="line.7"></a>
<FONT color="green">008</FONT>    <a name="line.8"></a>
<FONT color="green">009</FONT>    /**<a name="line.9"></a>
<FONT color="green">010</FONT>     * A variable that can be set only once.<a name="line.10"></a>
<FONT color="green">011</FONT>     * &lt;p&gt;<a name="line.11"></a>
<FONT color="green">012</FONT>     * An instance of this class is like a &lt;code&gt;final&lt;/code&gt; variable that can<a name="line.12"></a>
<FONT color="green">013</FONT>     * either be initialized, or left uninitialized. This is useful for keeping<a name="line.13"></a>
<FONT color="green">014</FONT>     * track of whether or not a particular branch of code has been executed. For<a name="line.14"></a>
<FONT color="green">015</FONT>     * example, say you've got some code that operates on a set of objects.<a name="line.15"></a>
<FONT color="green">016</FONT>     * Sometimes, the set is mutated, sometimes not. To remember whether or not a<a name="line.16"></a>
<FONT color="green">017</FONT>     * mutation was made, the set's update method could be coded as:<a name="line.17"></a>
<FONT color="green">018</FONT>     * &lt;/p&gt;<a name="line.18"></a>
<FONT color="green">019</FONT>     * &lt;pre&gt;<a name="line.19"></a>
<FONT color="green">020</FONT>     * private final Milestone&amp;lt;Boolean&amp;gt; dirty = Milestone.make();<a name="line.20"></a>
<FONT color="green">021</FONT>     * &amp;hellip;<a name="line.21"></a>
<FONT color="green">022</FONT>     * public void<a name="line.22"></a>
<FONT color="green">023</FONT>     * add(final Object x) {<a name="line.23"></a>
<FONT color="green">024</FONT>     *     objectSet.add(x);<a name="line.24"></a>
<FONT color="green">025</FONT>     *     dirty.set(true);<a name="line.25"></a>
<FONT color="green">026</FONT>     * }<a name="line.26"></a>
<FONT color="green">027</FONT>     * &lt;/pre&gt;<a name="line.27"></a>
<FONT color="green">028</FONT>     * &lt;p&gt;<a name="line.28"></a>
<FONT color="green">029</FONT>     * When the code is done using the set, a commit() method can check to see if<a name="line.29"></a>
<FONT color="green">030</FONT>     * any updates need to be written:<a name="line.30"></a>
<FONT color="green">031</FONT>     * &lt;/p&gt;<a name="line.31"></a>
<FONT color="green">032</FONT>     * &lt;pre&gt;<a name="line.32"></a>
<FONT color="green">033</FONT>     * public void<a name="line.33"></a>
<FONT color="green">034</FONT>     * commit() {<a name="line.34"></a>
<FONT color="green">035</FONT>     *     if (dirty.is()) {<a name="line.35"></a>
<FONT color="green">036</FONT>     *         // write out the new set<a name="line.36"></a>
<FONT color="green">037</FONT>     *         &amp;hellip;<a name="line.37"></a>
<FONT color="green">038</FONT>     *     }<a name="line.38"></a>
<FONT color="green">039</FONT>     * }<a name="line.39"></a>
<FONT color="green">040</FONT>     * &lt;/pre&gt;<a name="line.40"></a>
<FONT color="green">041</FONT>     * &lt;p&gt;<a name="line.41"></a>
<FONT color="green">042</FONT>     * By using this class, instead of a normal variable, you can better communicate<a name="line.42"></a>
<FONT color="green">043</FONT>     * to a code reviewer that a variable is only assigned once. The variable<a name="line.43"></a>
<FONT color="green">044</FONT>     * declaration alone ensures this property is enforced, without the need to<a name="line.44"></a>
<FONT color="green">045</FONT>     * inspect all the code that can access the variable.<a name="line.45"></a>
<FONT color="green">046</FONT>     * &lt;/p&gt;<a name="line.46"></a>
<FONT color="green">047</FONT>     * &lt;p&gt;<a name="line.47"></a>
<FONT color="green">048</FONT>     * This class is named Milestone, since it keeps track of whether or not a<a name="line.48"></a>
<FONT color="green">049</FONT>     * program's execution reached a certain point or not. This program meaningful<a name="line.49"></a>
<FONT color="green">050</FONT>     * execution point is a milestone.<a name="line.50"></a>
<FONT color="green">051</FONT>     * &lt;/p&gt;<a name="line.51"></a>
<FONT color="green">052</FONT>     */<a name="line.52"></a>
<FONT color="green">053</FONT>    public class<a name="line.53"></a>
<FONT color="green">054</FONT>    Milestone&lt;T&gt; implements Equatable, Serializable {<a name="line.54"></a>
<FONT color="green">055</FONT>        static private final long serialVersionUID = 1L;<a name="line.55"></a>
<FONT color="green">056</FONT>        <a name="line.56"></a>
<FONT color="green">057</FONT>        /**<a name="line.57"></a>
<FONT color="green">058</FONT>         * current state<a name="line.58"></a>
<FONT color="green">059</FONT>         */<a name="line.59"></a>
<FONT color="green">060</FONT>        private T marker;<a name="line.60"></a>
<FONT color="green">061</FONT>    <a name="line.61"></a>
<FONT color="green">062</FONT>        protected<a name="line.62"></a>
<FONT color="green">063</FONT>        Milestone() {}<a name="line.63"></a>
<FONT color="green">064</FONT>        <a name="line.64"></a>
<FONT color="green">065</FONT>        /**<a name="line.65"></a>
<FONT color="green">066</FONT>         * Constructs an instance.<a name="line.66"></a>
<FONT color="green">067</FONT>         */<a name="line.67"></a>
<FONT color="green">068</FONT>        static public &lt;T&gt; Milestone&lt;T&gt;<a name="line.68"></a>
<FONT color="green">069</FONT>        make() { return new Milestone&lt;T&gt;(); }<a name="line.69"></a>
<FONT color="green">070</FONT>        <a name="line.70"></a>
<FONT color="green">071</FONT>        // org.joe_e.var.Milestone interface<a name="line.71"></a>
<FONT color="green">072</FONT>    <a name="line.72"></a>
<FONT color="green">073</FONT>        /**<a name="line.73"></a>
<FONT color="green">074</FONT>         * Has the milestone been {@linkplain #set passed}?<a name="line.74"></a>
<FONT color="green">075</FONT>         * @return &lt;code&gt;true&lt;/code&gt; if {@linkplain #set set},<a name="line.75"></a>
<FONT color="green">076</FONT>         *         else &lt;code&gt;false&lt;/code&gt;<a name="line.76"></a>
<FONT color="green">077</FONT>         */<a name="line.77"></a>
<FONT color="green">078</FONT>        public boolean<a name="line.78"></a>
<FONT color="green">079</FONT>        is() { return null != marker; }<a name="line.79"></a>
<FONT color="green">080</FONT>        <a name="line.80"></a>
<FONT color="green">081</FONT>        /**<a name="line.81"></a>
<FONT color="green">082</FONT>         * Gets the milestone marker.<a name="line.82"></a>
<FONT color="green">083</FONT>         * @return marker, or &lt;code&gt;null&lt;/code&gt; if not {@linkplain #set set}<a name="line.83"></a>
<FONT color="green">084</FONT>         */<a name="line.84"></a>
<FONT color="green">085</FONT>        public T<a name="line.85"></a>
<FONT color="green">086</FONT>        get() { return marker; }<a name="line.86"></a>
<FONT color="green">087</FONT>    <a name="line.87"></a>
<FONT color="green">088</FONT>        /**<a name="line.88"></a>
<FONT color="green">089</FONT>         * Sets the milestone marker, if not already set.<a name="line.89"></a>
<FONT color="green">090</FONT>         * @param marker    initialized value of the variable<a name="line.90"></a>
<FONT color="green">091</FONT>         * @return &lt;code&gt;false&lt;/code&gt; if previously set, else &lt;code&gt;true&lt;/code&gt;<a name="line.91"></a>
<FONT color="green">092</FONT>         */<a name="line.92"></a>
<FONT color="green">093</FONT>        public boolean<a name="line.93"></a>
<FONT color="green">094</FONT>        set(final T marker) {<a name="line.94"></a>
<FONT color="green">095</FONT>            if (null == marker) { throw new NullPointerException(); }<a name="line.95"></a>
<FONT color="green">096</FONT>            if (null != this.marker) { return false; }<a name="line.96"></a>
<FONT color="green">097</FONT>            this.marker = marker;<a name="line.97"></a>
<FONT color="green">098</FONT>            return true;<a name="line.98"></a>
<FONT color="green">099</FONT>        }<a name="line.99"></a>
<FONT color="green">100</FONT>    }<a name="line.100"></a>




























































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